A useful tip that I have used extensively, is to flush water lines with a material known as Chlorhexidine Gluconate .12%. This is commonly known as peridex mouth wash. If we can use it as a mouthwash it won’t have any adverse effects.
This may be done throughout the season, it is quite inexpensive and will kill off most bugs but in particular the coliform ones that cause so much grief in our bowels. Water quality is a major issue and once the bugs get in they can be difficult to get rid of.
This is particularly so with hot water lines which are great for the convenience but because they are heated bugs grow very quickly in them. The other suggestion I would offer is to make sure the water lines that are used for human use are thoroughly drained after flushing (at the end of the season) or if the boat will be left for a while, a dry tube will be very much less likely to breed bacteria than a wet one. The chlorhexidine will not attack plastics or any other materials to the best of my knowlege. I have used this material for this purpose for 25 years with no problems.
One of the best ways to dry water lines is simply to blow some compresed air thru them (if available).
Your local pharmacy likely does not carry Peridex, the mouthwash Stewart mentioned.
But your local supermarket or farmasi likely carries Oradex, a non-alcoholic mouthwash with 0.06% Chlorhexidine gluconate - half the potency of Peridex. Oradex comes in a handy 750 ml bottle, marked ‘for external use, do not swallow’. I’d guess that it’d be cheaper to buy in Malaysia than Singapore.
I reckon the black crap in the vent hose is a bacterial film. I think the bacterial film loves the humid conditions (water evaporating from the water tanks). And the problem is that when I fill the tanks, any overflow that runs up the vent hose washes down some of the bacterial film into the tanks.
On Zygote, I’ve adopted the same technique I use on the bacterial film that grows on my teeth - an occasional brushing. I’ve a plumber’s snake type gadget, with a tiny bottle brush on the business end.
Note that the accepted wisdom is not to use a low pH mouthwash (eg Listerine) because they strip dental enamel. And alcoholic mouthwashes are out of favor, because they are presumed to be associated with increased prevalence of mouth cancers (a debate is continuing on the issue: the mood today is against the alcoholic mouthwashes, but the final jury verdict is not likely soon). Chlorhexidine gluconate mouthwashes definitely keep oral bacterial levels low, but the bacterial films they kill often leave stains on the teeth. In a few decades time, we’ll know what daily exposure to Chlorhexidine gluconate does: a goodly number of people are involved in the experiment!
This business of waterline cleaning is thorny, the best thing is to not get the bugs in there in the first place but almost impossible to achieve. Physical cleaning of pipes and tanks should be the first line of attack,being careful not to scratch if possible. I know that people have used bleach etc and there likely is some merit to this but there is a cost too. Not great materials to be ingesting, the good news is that Chlorhexidine has been used for at least three decades and whilst it can stain pipes and teeth it seems to be ok. Doug please note it is point 12% not 12%. I suspect it will be freely available in your guys necks of the woods.